'protk.dat' file is needed to register Capital plugin in Creo. It is not included in Updates 2207.2406 and 2308.2406 in %CAPITAL_HOME%\adaptors\CreoPlugin\creo9\64b. However, it will be included in Update 2408.
Following are different workarounds for this:
1. Copy protk.dat file from creo/64gb folder to creo9/64gb and update EXEC_FILE and TEXT_DIR paths in protk.dat file according to creo9 folder as shown below:
EXEC_FILE C:/MentorGraphics/Capital/adaptors/CreoPlugin/creo9/64b/capital_plugin.dll
TEXT_DIR C:/MentorGraphics/Capital/adaptors/CreoPlugin/creo9/text
2. Copy creo9 protk.dat file from prior updates starting from 2312.
3. Install 2406 update on top of prior updates starting from 2312.